1. Field of the Invention
This invention relates to a method and apparatus for indicating to a vehicle operator the range of transmission gears that are available for selection by the vehicle operator at the existing vehicle speed within a predetermined range of engine speeds and the engine speed at which the transmission may be shifted synchronously into each of the gears. This invention also relates to a method for calibrating the apparatus for virtually any vehicle equipped with a manual transmission.
2. Description of the Related Art
Heavy trucks generally employ manual transmissions having a relatively large number of gears. Such transmissions usually are non-synchromesh transmissions, which require that the driven gears and driving gears be rotated at very nearly the same speed before they can intermesh. Thus, for any particular vehicle speed, it is necessary to match the engine speed with the vehicle speed for the particular gear selected before that gear can be engaged.
In order to match engine speed with vehicle speed for a given gear ratio, it is usually necessary to "double clutch" the transmission. This procedure involves first shifting the transmission into neutral and then adjusting the engine speed up or down to match the intended gear and then depressing the clutch and shifting the transmission into that gear.
Experienced truck drivers usually get a feel for what transmission gears are available under normal driving conditions and what engine speeds are necessary to engage the gears. This is frequently a matter of sensitivity to the sound of the engine in comparison with vehicle speed. Inexperienced operators and even experienced operators in emergencies or under other stressful conditions (e.g., downhill acceleration) have difficultly in determining what gears are available for a particular vehicle speed.
A number of devices have been invented to assist the vehicle operator in shifting smoothly into the next higher or lower gear. One such device is disclosed in U.S. Pat. No. 4,320,381 to Olivier, wherein a display has a fixed set of numerals representing gear ratios and a rotatable pointer. When the pointer is aligned with one of the numerals, the particular gear associated with the numeral can be engaged. There is no indication in this patent if the engine RPM is within an acceptable range for shifting. The device is useful only for the particular transmission for which it is designed, and is not universally adaptable to other transmissions. U.S. Pat. No. 4,800,360 to Dunkley et al. discloses a vehicle display and control device for semi-blocked transmissions. The display is divided into a first section that indicates the presently engaged gear, a second section that indicates a number of gears available above the presently engaged gear, and a third section that indicates a number of gears that are available below the presently engaged gear. The Dunkley et al. patent takes control of the shifting operation when a joystick is manipulated by a vehicle operator. As in the Olivier patent, the Dunkley et al. patent is not universally adaptable to manual multi-gear transmissions and does not visually indicate when a chosen target gear exceeds the permissible engine speed range.